AC Motor Speed Controller

This AC motor speed controller can handle most universal type (brushed) AC motors and other loads up to about 250W. It works in much the same was a light dimmer circuit; by chopping part of the AC waveform off to effectively control voltage. Because of this functionality, the circuit will work for a wide variety of loads including incandescent light bulbs, heating elements, brushed AC motors and some transformers. The circuit tries to maintain a constant motor speed regardless of load so it is also ideal for power tools. Note that the circuit can only control brushed AC motors. Inductive motors require a variable frequency control.

Schematic

Parts

Part

Total Qty.

Description

Substitutions

R1

1

27K 1W Resistor

R2

1

10K 1/4W Resistor

R3

1

100K 1/4W Resistor

R4

1

33K 1/4W Resistor

R5

1

2.2K 1/4W Resistor

R6

1

1K 1/4W Resistor

R7

1

60K Ohm 1/4W Resistor

R8

1

3K Linear Taper Trim Pot

R9

1

5K Linear Taper Pot

R10

1

4.7K Linear Taper Trim Pot

R11

1

3.3K 1/4W Resistor

R12

1

100 Ohm 1/4W Resistor

R13

1

47 Ohm 1W Resistor (See Notes)

C1, C3

2

0.1uF Ceramic Disc Capacitor

C2

1

100uF 50V Electrolytic Capacitor

D1

1

6V Zener Diode

Q1

1

2N2222 NPN Transistor

2N3904

SCR1

1

ECG5400

TR1

1

TRIAC (See Notes)

U1

1

DIAC Opto-Isolator (See Notes)

BR1, BR2

2

5A 50V Bridge Rectifier

T1

1

Transformer (See Notes)

MISC

1

PC Board, Case, Line Cord, Socket For U1, Heatsinks

Notes

TR1 must be chosen to match the requirements of the load. Most generic TRIACs with ratings to support your load will work fine in this circuit. If you find a TRIAC that works well, feel free to leave a comment.

U1 must be chosen to match the ratings of TR1. Most generic DIAC based opto-isolators will work fine. If you have success with a specific part, feel free to leave a comment.

T1 is any small transformer with a 1:10 turns ratio. The circuit is designed to run on 120V so a 120V to 12V transformer will work. Alternately, you can wind T1 on a transformer core using a primary of 25 turns, a secondary of 200 turns, and 26 gauge magnet wire.

R9 is used to adjust motor speed. R10 is a trim pot used to fine tune the governing action of the circuit. R8 fine tunes the feedback circuit to adjust for proper voltage at the gate of SCR1. It should be adjusted to just past the minimum point at which the circuit begins to operate.

R13 must be chosen to match the load. Generally, larger loads will require a smaller value.

Since this circuit is not isolated from mains, it must be built in an insulated case.

dear sir,i have an ac induction motor drive and also have a input circuit (i use previousely to operate a dc motor),but the problem is it not works on ac drive.can u suggest on it.
i can provide technical detail and pictures of entire system.
waiting for ur early reply.

About the diac used in the speed controller( to the person looking for a match to the triac) Diacs are not much different depending on the part # they only severe to allow the triac to trigger symetrically in both polarities of gate signal. They will not pass current until the gate trigger signal rises above the mid twenty volt range in either +/- voltage.

this site is very useful for all the persons not only for techno grads but also for every one who are interested in electrical machines which is one of the challenging subject it also helps in improving knowledge

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